This injector O-ring seals the interface between the injector body and the cylinder head in the fuel system of the host tractor. It prevents compression leakage and fuel blow-by, which would otherwise cause a loss of cylinder pressure and erratic injection timing. The ring is compressed into a machined groove in the injector bore; a worn or hardened O-ring allows combustion gases to escape, producing a ticking sound and reducing engine power. As an original AGCO component, the O-ring is molded to the same cross-section and durometer as the factory seal, so it seats fully in the groove without requiring additional sealant. Replace the O-ring whenever the injector is removed for servicing.